1. Field of the Invention
The present invention relates to light emitting diode (LED) displays. In particular, the present invention relates to surface mounted light emitting diodes with illuminated segments.
2. Description of the Related Art
Light emitting diodes (LEDs) are commonly used in display devices. LED displays typically have segments that are illuminated with one or more LED chips to display information. Digital characters can be divided into seven segments, and the luminescence of different segments can be combined to display different numerical values. LED displays are commonly used on control panels such as appliance controls for ovens, microwaves, dishwashers, and etc.
A typical problem with LED displays is to distribute the light emitted by the small LED chip over the entire segment to be displayed. The area of a light emitting region of an LED chip is usually less than 1 mm2 while the area of the segment to be illuminated is usually more than 1 mm2. In many applications, the segment shape is not the same shape as the LED chip. For example, a rectangle segment has a larger length than width while typical LED chip is circular or square. The result is often a segment with non-uniform illumination. The area of the segment directly above the LED chip usually has a greater illumination than the rest of the segment. A greater illumination in one area is often referred to as a “hot spot.” Common solutions to produce a more uniform display involve using multiple LED chips within one segment or using a diffusion layer above the LED chip to scatter the light. However, using multiple LED chips in one segment increases the complexity and cost than using only one LED chip. On the other hand, using a diffusion layer to scatter the light tends to be more economical. However, if a diffusion layer is used, the distance between the LED chip and the light exit surface of the segment is relatively large to produce enough diffraction of the light to uniformly illuminate the segment.
An LED device is often mounted to a front support plate to form an LED display. The front support plate can be a printed circuit board (PCB). If a diffusion layer is used, the thickness of the PCB is determined by the distance between the LED chip and the light exit surface of the segment. The distance between the LED chip and the light exit surface is typically greater than necessary for the thickness of a PCB without an LED device. The distance for substantial uniform illumination adds to both the total thickness of the LED display and the cost of the PCB. In addition, the PCB often covers substantially the entire control panel on an appliance while the LED display is only a small portion of control panel. Therefore, the entire PCB thickness is increased due to the LED display.